The objective of this project is to isolate, characterize and determine the mechanisms of action of certain factors, present in serum, that are required for growth and cell division of mammalian cells. Our major goal for the coming year is to understand the factors involved in density dependent regulation of growth. The decrease in receptor sites for EGF observed with BSC-1 cells will be studied carefully. Density-dependent decreases in uptake of glucose and glutamine will be studied, because of evidence that these two nutrients have pronounced growth regulatory roles in BSC-1 cells. Suggestive evidence that still other factors play a role in density dependent regulation of growth will be pursued.